1. Field of the Invention
The present invention relates to the structure of an optical waveguide device that functions while a functional component for performing optical branching, coupling, switching, and the like is inserted in the path of an optical waveguide and, more particularly, to a structure for facilitating manufacture of such a device which has a small transmission loss in an insertion region of the functional component.
2. Related Background Art
An optical device that performs optical branching, coupling, switching, and the like in a small region on an millimeter-order is a very important constituent element for downsizing or increasing the degree of functions of an optical communication system, an optical sensor, or the like. As such an optical device, a so-called parts insertion type optical waveguide device which functions by inserting a functional component for performing optical functions such as optical branching, coupling, switching, and the like in an optical waveguide has been attracting attention in recent years.
In this optical waveguide device, functions such as optical branching, coupling, and the like are conventionally realized by fabricating a directional coupler or an optical waveguide pattern having a structure of, e.g., a Y- or X-shaped waveguide, on a waveguide substrate. The switching function is realized by varying the propagation constant of the directional coupler.
Other than the method described above, the functions of branching, coupling, switching and the like of the optical waveguide device can be realized by incorporating a functional component that performs branching, coupling, switching, and the like in the path of the optical waveguide formed on the waveguide substrate.
FIG. 1 shows the arrangement of a conventional parts-insertion type optical waveguide device for realizing the optical branching function. In this conventional optical waveguide device, a half mirror 2 serving as a functional component for separating light is inserted at the intersecting portion (an insertion region where the functional component is to be inserted) of a T-shaped optical waveguide 1. The half mirror 2 has an angle of 45.degree. with respect to the optical path of the light to be incident on it. In the conventional optical waveguide device, the core width of the optical waveguide 1 is constant (the refractive index difference between the core and the cladding layer is also constant). In this arrangement, light propagating through an incident side optical waveguide 1a (the incident side of the half mirror 2) is separated into a transmission-side optical waveguide 1b (the exit-side optical waveguide of the half mirror 2) and a reflection-side optical waveguide 1c (the reflection-side optical waveguide of the half mirror 2) by the half mirror 2.
The manufacturing steps of this conventional optical waveguide device will be described. Part of the intersecting portion (the insertion region where the functional component is to be inserted) of the T-shaped optical waveguide 1 formed in advance on the optical waveguide substrate (a portion indicated by a rectangle in FIG. 1) is removed with a laser beam or the like to form a space for inserting the half mirror 2 therein. Then, the half mirror 2 as the functional component is inserted.
The conventional optical waveguide device is manufactured by performing the above manufacturing steps.